Image-receiving material for the production of photographic images by the silver salt diffusion process



United States Patent Ofilice 3,368,896 Patented Feb. 13, 1968 3,368,896 IMAGE-.\E(IEIVENG MATERIAL FOR THE PRO- DUCTIGN OF PHOTOGRAPHIC IMAGES BY THE SXLVER SALT DIFFUSION PRUCESS Alexander Riehel and Hans Ulrich, Leverlrusen, Wolfgang Himmelmann, Cologne-tamn1hein1, and Kari-Heinz Brita, Leverkusen, Germany, assignors to Afga Aktiengeselischaft, lLeverkusen, Germany, a corporation of Germany No Drawing. Filed June 26, 1963, Ser. No. 290,603 Claims priority, application Germany, July 28, 1962, A 40,836 8 Claims. (Cl. 06-29) The invention relates to an image-receiving material for the production of photographic images by the silver salt diffusion process. According to this known process, a light-sensitive silver halide emulsion layer (negative layer) is developed, while in the contact with a layer of a suitable image-receiving material (positive layer) by means of an alkaline developer mixture in the presence of a solvent for silver halide. Unexposed silver halide is dissolved from the negative layer, diffuses into the positive layer and is transformed into a silver image at the development nuclei present in the latter layer. When this is complete, the two layers are separated by pulling them apart.

The facility with which the two layers may be separated depends substantially on the choice of the coating media for the negative and positive layers. For example, if gelatine is used for both layers, they adhere very firmly one to another and they must quickly be separated one from another, whereas addition of a cellulose ester enables the layers to be separated more easily and after a much longer period of contact. Other substances which substantially facilitate the separation of the layers after the diffusion are known from British Patent No. 687,751, according to which a variety of materials, including polyamides, polyesters, polyvinyl alcohol, polyvinyl acetates and polyvinyl pyrrolidones can be employed.

Furthermore, British Patent No. 856,792, describes transfer foils with a transparent support, and image-receiving layers which contain, as binder, mixtures of alkylvinyl ether maleic anhydride copolymers with hydrophobic resins, such as cellulose derivatives. These layers have the disadvantage, however, that separate processing steps are necessary to produce the water-absorption capacity.

As layer formers, it is mainly proteins, such as gelatine or casein, which have been used in the art. The known modified-protein layers do not, however, satisfy all requirements. For example, the moist image-receiving lay ers, after the image has been produced and after separation from the light-sensitive material, are alkaline because they contain developer residues. As a result the white portions of the image show a tendency to yellow discoloration on keeping. Finally, the proteins develop tensile forces when completely dried and these forces result in curling of the papers.

It has now been found that the properties of imagereceiving layers, that contain a hydrophilic film-forming protein, such as gelatine or casein, are considerably improved if they have incorporated therein in dispersed form a copolymer of alkyl vinyl ethers and maleic anhydride, the anhydride groups of which have been transformed, into semi-ester and semi-amide groups by reaction with lower aliphatic alcohols and monoalkanolamines.

By the inclusion of these copolymers into the protein layers the possible contact time between negative and positive during the processing is considerably increased, so that the negative and positive do not have to be separated withing a certain, relative short time. The processing thus becomes much more simple.

Because of the carboxyl groups and, possibly, the unreacted acid anhydride groups which are present in the copolymer, it acts as an alkali acceptor." In contrast to additive-free layers, the layers according to the invention show a neutral reaction imediately after the separation. As a result, yellowing of the material is largely prevented. The new image-receiving layers also show far less tendency to curl, presumably because addition of the copolymer in the form of a dispersion reduces the tension forces of the colloids in the hydrophilic layer.

A further advantage of the new image-receiving layers is the more rapid drying, which is a result of the relatively small proportion of hydrophilic colloid per unit area.

It is particularly simple to cast the materials according to the invention, since the viscosity of the casting solution is greatly reduced by the addition of the copolymer.

The copolymers, from which are made the additives used according to the invention, are obtained in a manner known per so by copolymerising maleic anhydride with alkyl vinyl ethers.

As alkyl vinyl ethers, there are advantageously used the vinyl ethers of lower aliphatic, monohydric saturated alcohols having 1 to 5 carbon atoms, more especially nbutyl vinyl ether or isobutyl vinylether. The copolymers advantageously contain the said components in approximately equimolar quantities, and generally have molecular weights from 800 to 3000.

In order to produce the additives of the present invention these copolymers may be reacted, at elevated temperatures in alcoholic solution, with an alcohol and a monoalkanolamine whereby the anhydride groups are partially or completely transformed into semi-ester and semi-amide groups. Suitable alcohols are monohydric, aliphatic, saturated alcohols with 1 to 3 carbon atoms, more especially methanol and suitable monoalkanolamines are such in which the alkanol group contains 2 to 4 carbon atoms. Monoethanolamine is advantageously used as the alkanolamine. The alkanolamines are generally applied in quantities of 0.1 to 5% by weight, calculated on the copolymer. The reaction may be carried out in a 120% solution of the copolymer in the aforementioned alcohols at temperatures of 50-120" (1., preferably at the reflux temperature of the solutions. The reaction products ob tained are insoluble in Water and are soluble in dilute alkalis and in aliphatic alcohols, such as methanol, propanol and butanol. Since the reaction products, in the form of their solutions in aliphatic alcohols, have a higher viscosity than corresponding material which has been produced exclusively with the use of the aforementioned alcohols, it is probable that the reaction leads to a crosslinking by the moneothanolamine or at least to a substantial increase in the molecular weight of the copolymers.

T he modified copolymers according to the invention are generally added in quantities from 5 to 200%, advantageously 10 to by weight, calculated on the weight of the film-forming protein. In order to produce the casting solution for forming the image-receiving'layer, the modified copolymers are first of all dissolved inan organic solvent such as butanol, together with a difiicultlyvolatile, oily dispersion auxiliary, such as a phthalicacid ester, and the solution obtained is dispersed, by means of a high-speed turbo-stirrer, in an aqueous solution of the protein.

A copolymer suitable for use in the present invention may be produced as follows:

10 kg. of maleic anhydride and 50 g. of benzoyl peroxide are dissolved in l. of benzene which has been 7 dried by distillation, in a 250 litre stirrer-type vessel under an atmosphere of nitrogen and are heated to just below the boiling point while stirring. 2 kg. of freshly distilled n-butyl-vinyl ether are then added in one portion; a reaction which causes the benzene to boil takes place within minutes. A further 8 kg. of freshly distilled n-butyl vinyl ether are then added, while stirring, at such a rate that the benzene boils quietly. After addition is complete the mixture is stirred under reflux for another 2 hours. After cooling, the precipitated polymer is collccted, roughly comminutcd, dried in vacuo at 35 to 50 C., and ground. The viscosity (10 g., dissolved in 100 ml. of acetone at C.) is between 3 and 4.5 cp. Yield :18 kg. =93%. Instead of n-butyl-vinyl other there may also be used methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether or isobutyl vinyl ether in equimolecular quantities.

10 kg. of this product are stirred into a cold mixture of 100 litres of methanol and 70 g. of monoethanolamine; the mixture is boiled under reflux for 2 hours and the resulting solution, after cooling, is stirred into at least 300 litres of water. The precipitated polymer is granulated while moist and dried in vacuo at to C. The quantity of monoethanolamine can be varied between 50 g. and 500 g. Yield =95--99%.

According to one preferred form of the invention, polymeric hardeners which are superior to the known monomeric hardeners such as formaldehyde, are added to the layers. Concerned here more especially are bisulphite compounds of polyacrolein which have been described in British Patent No. 797,459 and which may be applied according to the prescription given in Belgian Patent No. 624,108.

Oxidation products of carbohydrates are also suitable, for example the so-called dialdehyde starches which are described in British Patent No. 891,221 and also polyvinyl alcohol maleates, which are known from British Patent No. 822,061. A transfer material with particularly advantageous properties is obtained if the polymeric hardener is added both to the baryta-coating layer and to the image-receiving layer, hydrophobic film-forming products being used as binding agent for the barytacoating layer. Suitable as dialdehyde starch is, for example, the product marketed by Messrs. Miles Lab. Co. under the trade name Sunistar. It is used in an aqueous sodium acetate solution.

All known substances can be used as development nuclei for the transfer layer, for example colloidal silver or gold, thiourea, and the colloidal sulphides or selenides of silver, gold, lead, mercury, tin, zinc or copper. The development nuclei can be added to the casting solution as colloidal solutions or can be produced in the prepared layer by known processes. The nuclei are advantageously used in quantities from 0.001 to 1 g. per litre of casting solution. In addition, compounds which influence the image tone, such as mercaptobenzthiazolcs, mercaptotetrazoles or hydroxymercaptotriazines, as well as developer substances such as hydroquinone and silver halide solvents such as alkali or alkaline earth thiosulphates can be added to the positive layer.

The advantages obtained by using the additives accord ing to the invention are also obtained in those materials in which the negative and positive layers are cast one above the other on a support. It is immaterial here whether the negative layer is on top of the positive layer or vice versa.

Example 1 A solution of l g. of a 1:1 copolymer of maleic anhydride and n-butyl-vinyl ether, which is prepared and reacted in the manner described above, in a mixture of 5 ml. of n-butanol and 1 ml. of dibutyl phthalate, is run into 170 ml. of a 6% gelatine solution, which contains 0.003 g. of silver sulphide in colloidal form and 6 g. of sodium thiosulphate, using a high-speed turbo-stirrer with high speeds of revolution and strong shearing forces, so that a uniform emulsion is obtained. 1 ml. of a 10% solution of a bisulphite compound of polyacrolein is added 4- to this mixture. The casting solution thus prepared is cast in known manner onto ordinary or baryta-coatcd paper and dried.

The positive material is guided, in contact with an exposed silver halide emulsion layer (negative layer) prepared in the usual manner, through one of the known continuous-developing apparatuses, which contains the following developer solution:

Water ml 1000 p-Mcthylamino phenol sulphate g 1.5 Hydroquinone g 15 RBI g 2 Na SO g 10" NaOH g 15 After 10 to 20 seconds, the two layers are separated and an image with good density is obtained on the positive layer. The contact time can be increased to 2 minutes.

Exam pic 2 The process described in Example 1 is followed, using 6 g. of ccpolymer dissolved in 30 ml. of n'butanol and 6 ml. of dibutyl phthalate, emulsified into a gclatine solution. After development, the positive layer and negative layer can still satisfactorily be separated one from another after a contact time of 5 minutes. In addition, the resistance to yellowing of the prepared copy is substantially improved over a copy not containing the additive.

Example 3 A solution of l g. of copolymer in a mixture of 5 ml. of n-butanol and 1 ml. of dibutyl phthalate is emulsified, in ml. of a 6% aqueous neutral casein solution with additions of development nuclei and silver halide solvents as in Example 1. The hardening, as well as the casting and processing, is carried out according to Example 1. An image of good density is obtained on the positive layer. The positive and negative layers can still satisfactorily be separated after a contact time of 2 minutes.

Example 4 The process of Example 3 was followed but with 6 g. of copolymer dissolved in 30 ml. of n-butanol and 6 mi. of dibutyl phthalate. A hardener of the type described in Example 1 is also added. The contact time between positive and negative layers can thereby be extended to 5 minutes.

Example 5 A baryta coating, the binding agent of which consists of a hydrophobic, synthetic resin, for example of copolymers of acrylic acid esters, and which contains barium sulphate in normal concentrations is applied to a paper web. The baryta coating can contain also the usual additives such as white toners and wetting agents. As hardener, bisulphite compounds of polyacrolein, such as those described in Example I, are added to the baryta coating. From 500 to 1000 ml. of an aqueous 10% hardener solution are used to 30 litres of baryta casting solution which contains from 10 to 20% of binding agents.

The image-receiving layer described in Example 1 is applied to the dried baryta coating, the paper is processed photographically in the same manner and a positive image of excellent quality is obtained. Satisfactory separation of the negative and positive materials is possible even after relatively long contact times.

The transfer material described above is characterised by an excellent bonding, more especially between the baryta coating and the transfer layer.

What we claim is:

1. In an image-receiving protein layer having dispersed nucleating particles for the production of photographic images by the silver salt diffusion process, the improvement according to which there is l'icterogcncously dispersed in the protein layer a maleic anhydride-alkyl vinyl ether copolymer that has been at least partially transformed to semi-ester and semi-amide by reaction with a low molecular weight alkanol and with a monoalkanolamine, the reacted copolymer being in an amount from about 5 to about 200% calculated on the Weight of the protein.

2. The combination of claim 1 in which the reaction was carried out with about 0.1 to about 5% monoalkanolamine based on the weight of the unreacted polymer, the monoalkanolamine and the unreacted polymer being dissolved in the low molecular weight alkanol.

3. The combination of claim 1 wherein the protein in the image-receiving layer is gelatine.

4. The combination of claim 1 wherein the protein in the image-receiving layer is casein.

5. The combination of claim 1 wherein the image-receiving layer additionally contains a polymeric hardener for the protein.

6. The combination of claim 5, wherein the polymeric hardener is a bisulphite of polyacrolein.

7. The combination of claim 1 in which the image- 2 receiving layer is held on a baryta layer carried by a paper support, the baryta layer having as binding agent a hydrophobic film former and also containing a polymeric hardener for the protein of the image-receiving layer.

8. The combination of claim 7 wherein the hardener is a bisulphite of polyacrolein.

References Cited UNITED STATES PATENTS 2,558,857 7/195 1 Land 96-29 2,607,762 8/1952 Bowen 26029.6 3,017,377 1/ 1962 Kuhn 26029.6

FOREIGN PATENTS 1,083,051 6/1960 German.

856,792 12/ 1960 Great Britain.

NORMAN G. TORCHIN, Primary Examiner. DONALD LEVY, Examiner.

J. P. BRAMMER, Assistant Examiner. 

1. IN AN IMAGE-RECEIVING PROTEIN LAYER HAVING DISPERSED NUCLEATING PARTICLES FOR THE PRODUCTION OF PHOTOGRAPHIC IMAGES BY THE SILVER SALT DIFFUSION PROCESS, THE IMPROVEMENT ACCORDING TO WHICH THERE IS HETEROGENEOUSLY DISPERSED IN THE PROTEIN LAYER A MALEIC ANHYDRIDE-ALKYL VINYL ETHER COPOLYMER THAT HAS BEEN AT LEAST PARTIALLY TRANSFORMED TO SEMI-ESTER AND SEMI-AMIDE BY REACTION WITH A LOW MOLECULAR WEIGHT ALKANOL AND WITH A MONOALKANOLAMINE, THE REACTED COPOLYMER BEING IN AN AMOUNT FROM ABOUT 5 TO ABOUT 200% CALCULATED ON THE WEIGHT OF THE PROTEIN. 